Oxidative coupling
of methane (OCM) is a reaction to directly convert
methane into high value-added hydrocarbons (C2+) such as
ethylene and ethane using molecular oxygen and a catalyst. This work
investigated lanthanum oxide catalysts for OCM, which were promoted
with alkaline-earth metal oxides (Mg, Ca, Sr, and Ba) and prepared
by the solution-mixing method. The synthesized catalysts were characterized
using X-ray powder diffraction, CO2-programmed desorption,
and X-ray photoelectron spectroscopy. The comparative performance
of each promoter showed that promising lanthanum-loaded alkaline-earth
metal oxide catalysts were La-Sr and La-Ba. In contrast, the combination
of La with Ca or Mg did not lead to a clear improvement of C2+ yield. The most promising LaSr50 catalyst exhibited the highest
C2+ yield of 17.2%, with a 56.0% C2+ selectivity
and a 30.9% CH4 conversion. Catalyst characterization indicated
that their activity was strongly associated with moderate basic sites
and surface-adsorbed oxygen species of O2
–. Moreover, the catalyst was stable over 25 h at a reactor temperature
of 700 °C.
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